Method for purifying gas containing hydrocarbons

ABSTRACT

This invention relates to a process of cleaning gas, in particular hydrocarbonaceous gas such as e.g. natural gas, which is contaminated with sulfur in the form of H 2 S and mercaptans as well as CO 2 .  
     To create an improved process of cleaning hydrocarbonaceous gas, in which the energy consumption and hence the costs for generating a feed gas rather rich in H 2 S for the Claus plant can be decreased distinctly, it is proposed in accodance with the invention that before the absorption and regeneration plant ( 23 ) operated at a pressure of the feed gas of 20-80 bar abs another absorption plant ( 21 ) is provided, which operates with a selective solvent at the same pressure of 20-80 bar abs and which roughly desulfurizes the feed gas to 100-10,000 ppmV H 2 S, a solvent stream ( 17 ) loaded with hydrogen sulfide being withdrawn from this preceding absorption plant ( 21 ) and being supplied to a succeeding regeneration ( 22 ), that from the preceding absorption plant ( 21 ) a third gas stream ( 2 ), the roughly desulfurized crude gas, is supplied to the absorption and regeneration plant ( 23 ), and from this absorption and regeneration plant ( 23 ) the valuable gas ( 5 ) is withdrawn, which is supplied to a further use.

This invention relates to a process of cleaning gas, in particularhydrocarbonaceous gas such as e.g. natural gas, which is contaminatedwith sulfur in the form of H₂S and mercaptan as well as CO₂.

The document WO 97/26069 describes a process of cleaning gasescontaining carbon dioxide and sulfur, in which there aresulfur-contaminated impurities in the form of mercaptans and H₂S. In afirst absorption, the sulfur-contaminated impurities are removed fromthe gas, in order to produce a clean gas stream and a sour gas stream,the sour gas being hydrogenated in order to convert a major amount ofmercaptans to H₂S. The hydrogenated sour gas is introduced into a secondabsorption/regeneration plant, in which the sour gas is separated into afirst gas stream rich in H₂S, which is introduced into a Claus plant,and a second gas stream containing little H₂S, which is supplied to thepostcombustion. The Claus plant is followed by a tail gasaftertreatment, in wich the H₂S is reduced further and a gas rich in H₂Sis withdrawn.

Another unpublished application describes a process for removing theundesired sulfur-containing substances in the form of H₂S and mercaptanfrom crude gas. Crude gas is introduced into an absorption andregeneration column and washed therein, three gas streams beingwithdrawn from this absorption and regeneration column. A first exhaustgas stream is introduced into a Claus plant, a second sour gas streamwith a low concentration of H₂S is introduced into another absorptionplant, and a third gas stream, the valuable gas with the mercaptans, iscooled and supplied to an adsorption plant. From this adsorption plant,a cleaned valuable gas is withdrawn and a gas stream containingmercaptan is subjected to washing, which is then supplied to the Clausplant.

What is disadvantageous in these processes is the considerable effortfor raising the H₂S content of the exhaust gas of the first washingstage operating at high pressure, which removes both the H₂S containedin the feed gas and the entire CO₂, such that an easy and economicallyexpedient generation of sulfur in the Claus plant is possible. There isrequired a second absorption plant, whose operation for reprocessing thesolvent used consumes very much energy. The operation of this absorptionplant, and in particular the adjustment with the other plant components,is very expensive and complicated.

It is the object underlying the invention to create an improved processfor cleaning hydrocarbonaceous gas, in which the energy consumption andthus the costs for generating a feed gas as rich in H₂S as possible forthe Claus plant can distinctly be decreased.

In accordance with the invention, this object is solved in that beforethe absorption and regeneration plant operated at a pressure of the feedgas of 20-80 bar abs. another absorption plant is provided, whichoperates at the same pressure of 20-80 bar abs. with a selective solventand roughly desulfurizes the feed gas to 100-10,000 ppmV H₂S, a solventstream loaded with hydrogen sulfide being withdrawn from this precedingabsorption plant and being supplied to a succeeding regeneration, thatfrom the preceding absorption plant a third gas stream, the roughlydesulfurized crude gas, is supplied to the absorption and regenerationplant, and from this absorption and regeneration plant the valuable gasis withdrawn, which is supplied to a further use.

Due to the rough preliminary desulfurization by the preceding absorptionplant, the first small gas stream, which is supplied from theregeneration plant to the Claus plant, consists of up to 95 vol-%hydrocarbon and up to 30 vol-% carbon dioxide. The second gas stream,which is supplied from the regeneration plant to the Claus plant,consists of 20 to 90 vol-% hydrogen sulfide, maximally 80 vol-% carbondioxide, and small amounts of mercaptan.

Due to the fact that from the preceding absorption column a solventstream highly loaded with H₂S is withdrawn and supplied to theregeneration plant, the solvent stream is by 30 to 60% smaller than inaccordance with the prior art, depending on the plant configuration.Thus, the energy consumption for the regeneration likewise is smaller by30 to 60%.

The roughly desulfurized crude gas is withdrawn from the precedingabsorption column as second gas stream and supplied to a second washingstage comprising absorption and regeneration. Since in this secondwashing stage only a very small amount of H₂S must be washed out apartfrom CO₂, the required amount of solvent also is distinctly smaller herethan in the prior art, namely 20 to 70% smaller in dependence on theH₂S/CO₂ ratio, so that here as well 45% less regeneration energy isrequired.

As preferred solvent of the preceding absorption plant, there istypically used methyldiethanolamine (MDEA).

The preceding, selective absorption plant is configured such that besidea rather large amount of H₂S a rather small amount of CO₂ is absorbed.It is known that in the case of the solvent MDEA the absorption of CO₂is limited by the absorption rate, so that it can be minimized by onlybriefly bringing the feed gas in contact with the solvent MDEA. Thecontact time necessary for the absorption of H₂S decreases withincreasing pressure of the feed gas and at a pressure of e.g. 50 barabs. lies in the range of up to 20 seconds.

As product, there is obtained a gas which has a low content of H₂S(typically 100-10,000 ppmV), but still contains a large part of the CO₂contained in the feed gas. Both the CO₂ and the remaining small amountof H₂S then are completely removed from the valuable gas in thesucceeding high-pressure washing stage and discharged as exhaust gastogether with a part of the mercaptan contained in the feed gas. Thedegree of sulfur recovery of the entire plant is increased in that thisexhaust gas is introduced into the hydrogenation of the tail gas plant,in order to convert sulfur components into H₂S, and is then introducedinto the absorption plant of the tail gas plant.

Since the low H₂S content required for the valuable gas need only beachieved after this second high-pressure washing stage, the precedingabsorption plant can employ solvent which comes from the tail gaswashing stage of the Claus plant and already contains H₂S and CO₂. Thetotal amount of MDEA solution to be reprocessed in a regeneration thusis minimized. Alternatively, unloaded solvent can also be used. The H₂Sconcentrations in the exhaust gas supplied from the regeneration to theClaus plant, which can be achieved by a suitable configuration of theabsorption plant, are higher than those to be achieved in accordancewith the prior art, so that the Claus plant can be designedcorrespondingly smaller.

Embodiments of the process will be explained by way of example withreference to the drawing.

Via line (1), crude gas is introduced into a first absorption column(21), in which most of the H₂S contained is washed out. As solvent, asolvent stream (16) is supplied to the absorption column (21), whichsolvent stream was preloaded with H₂S and CO₂ in a succeeding tail gasabsorption plant (29).

From the absorption column (21), a solvent stream (17) highly loadedwith H₂S is withdrawn and supplied to a regeneration plant (22). Fromthe regeneration plant (22), a first small gas stream (3) is directlysupplied to the Claus plant (27). This exhaust gas stream (3) chieflyconsists of up to 95 vol-% hydrocarbon and up to 30 vol-% CO₂ with smallamounts of mercaptan (up to 0.3 vol-%) and H₂S (up to 5 vol-%).

A second, larger gas stream (4), which contains 20-90 vol-% H₂S, 10-80vol-% CO₂ and up to 3000 ppmV mercaptan, likewise is directly suppliedto the Claus plant (27). As further stream, an unloaded solvent stream(18) is withdrawn, which is supplied to the tail gas absorption plant(29). Should the amount of solvent required in the first absorptioncolumn (21) be larger than the one used in the tail gas absorption plant(29), it is also possible that via line (19) unloaded solvent isdirectly supplied from the regeneration plant (22) to the absorptioncolumn (21). Should the amount of solvent required in the firstabsorption column (21) be smaller than the one used in the tail gasabsorption plant (29), it is also possible that via line (20) preloadedsolvent is directly supplied from the tail gas absorption plant (29) tothe regeneration plant (22).

From the absorption column (21), a second gas stream (2), the roughlydesulfurized crude gas, is withdrawn and supplied to a second washingstage (23) comprising absorption and regeneration. The roughlydesulfurized crude gas (2) still contains a large part of the mercaptancontained in the crude gas, 100-10,000 ppmV H₂S and 50-95% of the CO₂contained in the crude gas. From this second washing stage (23), a firstgas stream (6) is withdrawn, which in one of the other partial plants(e.g. Claus plant (27) or hydrogenation (8) or for instance in a notrepresented exhaust gas postcombustion) is utilized as fuel gas or canbe discharged to the outside via line (30). This gas stream (6) chieflyconsists of up to 80 vol-% hydrocarbon and up to 20 vol-% CO₂ with smallamounts of mercaptan (up to 0.3 vol-%) and H₂S (up to 5000 ppmV). Assecond gas stream (5), the valuable gas with the largest part of themercaptan is withdrawn from the second washing stage (23) via line (5)and then e.g. cooled (24) and supplied to an adsorption (25) via line(8) for removing the mercaptan. A third gas stream from the absorptionplant (23), which contains up to 99.8 vol-% CO₂, up to 10 vol-% H₂S and0.2 vol-% mercaptan, is supplied to a hydrogenation (28) via line (7).

The Claus plant (27) is a plant known per se, which consists of acombustion furnace as well as a plurality of catalytic reactors forperforming the reaction. The liquid sulfur obtained is withdrawn vialine (16) and supplied to a further use. In the Claus plant (27), thereis always obtained a so-called residual Claus gas, which apart fromnon-condensed elementary sulfur contains unreacted sulfur dioxide andH₂S. This residual gas is withdrawn via line (13) and subjected to anaftertreatment, in order to increase the degree of sulfur recovery. Vialine (13), the residual Claus gas is supplied to a hydrogenation plant(28), which via line (7) is also supplied with the gas from the secondwashing stage (23). In the hydrogenation (28), mercaptan and SO₂ areconverted to H₂S and supplied to an absorption plant (29) via line (14).From the absorption plant (29), a solvent loaded with H₂S and CO₂ issupplied via line (16) to the first absorption column (21) for thefurther absorption of H₂S, before it is reprocessed in the regenerationplant (22) as described above and the entire H₂S obtained is supplied tothe Claus plant (27). In this way, a high degree of sulfur recovery isachieved.

The remaining gas only contains very little (up to 2000 ppmV) H₂S and iswithdrawn from the absorption plant (29) via line (15) and for instancesupplied to a combustion.

EXAMPLE

The following Table shows an analysis of the gas streams and the liquidprocess streams in the individual lines. Line No.: 1 2 3 Process CrudeRoughly Desulfurized First Let-down Gas Stream Stream Gas Crude Gas toClaus Plant Phase gas gas gas Components Nm³/h kg Mole/h ppm V Vol %Nm³/h kg Mole/h ppm V Vol % Nm³/h kg Mole/h ppm V Vol % CO2 21680 967,32,59 18645 831,85 2,25 5,24 0,23 0,98 N2 29102 1298,4 3.48 29093 1298,03,51 9,03 0,40 1,68 CH4 705460 31474,1 84,26 704982 31453 85,00 461,872,61 86,18 C2H6 45661 2037,1 5,45 45629 2035,7 5,50 29,41 1,31 5,49 C3H818593 829,5 2,22 18575 828,7 2,24 17,17 0,77 3,20 i-C4 2981 133,0 0,362981 133,0 0,36 0,57 0,03 0,11 n-C4 4333 193,3 0,52 4331 193,2 0,52 1,890,08 0,35 i-C5 1203 53,7 0,14 1203 53,7 0,15 0,21 0,01 0,04 n-C5 104046,4 0,12 1040 46,4 0,13 0,21 0,01 0,04 C6 cut 751 33,5 0,09 751 33,50,09 0,25 0,01 0,05 C7 cut 379 16,9 0,05 379 16,9 0,05 0,03 0,00 0,01 C8140 6,2 0,02 140 6,2 0,02 0,01 0,00 0,00 C9 93 4,1 0,01 93 4,1 0,01 0,050,00 0,01 H2S 5851 26103 0,699 401,4 17,91 484 0,05 5,41 0,24 1,01 COS2,5 0,11 3 0,0003 1,7 0,07 2 0,0002 0,01 0,00 20 0,00 CH3SH 21,8 0,97 260,0026 19,9 0,89 24 0,0024 0,13 0,01 250 0,03 C2H5SH 117,2 5,23 1400,0140 99,5 4,44 120 0,0120 0,63 0,03 1170 0,12 C3H7SH 47,7 2,13 570,0057 46,4 2,07 56 0,0056 0,29 0,01 540 0,05 C4H9SH 5,0 0,22 6 0,00065,0 0,22 6 0,0006 0,05 0,00 90 0,01 CS2 SO2 SX CO H2 O2 H2O saturated1019 45,48 0,12 3,49 0,16 0,65 Flow Nm³/h 837240 100,00 829433 100,00536 100,00 Flow kg/h 723091 709163 449 Flow Kgmole/h 37353 37005 24 FlowMMSCFD 750,00 743,01 0,480 Mole Wt Kg/Kg 19,36 19,16 18,77 mole Temp. °C. 10 42 29 Pressure bar 68,0 67,8 6,0 (abs) Density Kg/m³ Vap. Frac —1,0 1,0 1,0 Line No.: 4 5 6 Process Exhaust Gas Rich in Valuable GasSecond Let-down Gas Stream H_(s)S to Claus Plant for Gas Cooling StreamPhase gas gas gas Components Nm³/h kg Mole/h ppm V Vol % Nm³/h kg Mole/hppm V Vol % Nm³/h kg Mole/h ppm V Vol % CO2 5625,8 250,99 46,01 41 1,8150 0,005 72,63 3,24 18,59 N2 29087 1297,72 3,59 5,47 0,24 1,40 CH4 17,120,76 0,14 704689 31439,68 86,94 266,08 11,87 68,10 C2H6 2,45 0,11 0,0245600 2034,46 5,63 24,22 1,08 6,20 C3H8 1,22 0,05 0,01 18564 828,25 2,298,60 0,38 2,20 i-C4 2979 132,92 0,37 1,56 0,07 0,40 n-C4 4329 193,130,53 2,03 0,09 0,52 i-C5 1202 53,64 0,15 0,59 0,03 0,15 n-C5 1039 46,360,13 0,51 0,02 0,13 C6 cut 750 33,48 0,09 0,39 0,02 0,10 C7 cut 37916,91 0,05 0,16 0,01 0,04 C8 140 6,23 0,02 0,08 0,00 0,02 C9 93 4,140,01 0,04 0,00 0,01 H2S 6174,5 275,47 50,50 2,5 0,11 3 0,000 0,39 0,20,10 COS 0,8 0,04 69 0,01 0,4 0,019 1 0,00 0,01 0,00 20 0,00 CH3SH 1,70,08 141 0,01 16,5 0,738 20 0,00 0,11 0,00 280 0,03 C2H5SH 17,1 0,761395 0,14 82,6 3,686 102 0,01 0,59 0,03 1500 0,15 C3H7SH 1,0 0,04 810,01 44,6 1,990 55 0,01 0,21 0,01 540 0,05 C4H9SH 0,0 0,00 0 0,00 4,70,212 6 0,00 0,02 0,00 60 0,01 CS2 SO2 SX CO H2 O2 H2O 385 17,18 3,151528 68,17 0,19 7,05 0,31 1,80 Flow Nm³/h 12227 100,0 810572 100,0 391100,0 Flow kg/h 20818 672080 414 Flow Kgmole/h 545 36164 17 Flow MMSCFD10,953 726,111 0,350 Mole Wt Kg/Kg 38,16 18,58 23,74 mole Temp. ° C. 3550 47 Pressure bar 1,8 66,8 6,0 (abs) Density Kg/m³ Vap. Frac — 1,0 1,01,0 Line No.: 7 8 9 Process Exhaust Gas Rich in Cooled Valuable GasSweet Stream CO₂ to Hydrogenation to Mole Sieve Plant Gas Phase gas gasgas Components Nm³/h kg Mole/h ppm V Vol % Nm³/h kg Mole/h ppm V Vol %Nm³/h kg Mole/h ppm V Vol % CO2 18532 826,80 90,78 41 1,81 0,005 41 1,810,005 N2 29087 1297,72 3,59 29073 1297,07 3,60 CH4 26,54 1,18 0,13704689 31439,68 87,1 704337 31423,96 87,12 C2H6 4,08 0,18 0,02 456002034,46 5,64 45578 2033,44 5,64 C3H8 2,04 0,09 0,01 18564 828,25 2,2918550 827,63 2,29 i-C4 2979 132,92 0,37 2978 132,85 0,37 n-C4 4329193,13 0,53 4327 193,03 0,54 i-C5 1202 53,64 0,15 1202 53,61 0,15 n-C51039 46,36 0,13 1039 46,34 0,13 C6 cut 750 33,48 0,09 749 33,42 0,09 C7cut 379 16,91 0,05 377 16,82 0,05 C8 140 6,23 0,02 138 6,16 0,02 C9 934,14 0,01 89 3,95 0,01 H2S 398,6 17,78 19525 1,95 2 0,11 3 0,00 2,50,110 3 0,00 COS 1,22 0,05 60 0,01 0 0,02 1 0,00 0,04 0,0019 1 0,00CH3SH 3,27 0,15 160 0,0, 17 0,74 20 0,002 0,2 0,011 0,3 0,00 C2H5SH16,33 0,73 800 0,08 83 3,69 102 0,01 1,4 0,063 1,7 0,0002 C3H7SH 1,630,07 80 0,01 45 1,99 55 0,006 0,7 0,030 0,8 0,0001 C4H9SH 0,20 0,01 100,00 5 0,21 6 0,001 0,01 0,004 0,1 0,000 CS2 SO2 SX CO H2 O2 H2O 142863,71 7,00 144 6,43 0,02 1 0.04 1,0 0,0001 Flow Nm³/h 20414 100,0 809188100,0 808481 100,0 Flow kg/h 38232 670968 670035 Flow Kgmole/h 911 3610236070 Flow MMSCFD 18,287 725 724,237 Mole Wt Kg/Kg 41,98 19 18,58 moleTemp. ° C. 50 10 25 Pressure bar 1,8 66,5 65,2 (abs) Density Kg/m³ Vap.Frac — 1,0 1 1,0 Line No.: 10 11 12 Process Gas Stream Fuel Gas EnrichedMercaptan Gas Stream Containing Mercaptan to Plant Boundary to ClausPlant Phase gas gas gas Components Nm³/h kg Mole/h ppm V Vol % Nm³/h kgMole/h ppm V Vol % Nm³/h kg Mole/h ppm V Vol % CO2 N2 7814,5 348,6529,27 7812,2 348,54 29,55 2,3 0,10 0,80 CH4 18552,3 827,71 69,49 18447822,99 69,78 105,7 4,72 36,13 C2H6 22,8 1,02 0,09 22,3 1,00 0,08 0,50,02 0,16 C3H8 13,9 0,62 0,05 11,9 0,53 0,05 2,0 0,09 0,68 i-C4 1,5 0,070,01 1,0 0,05 0,00 0,4 0,02 0,15 n-C4 2,2 0,10 0,10 1,8 0,08 0,01 0,040,02 0,12 i-C5 0,6 0,03 0,00 0,3 0,01 0,00 0,3 0,02 0,12 n-C5 0,5 0,020,00 0,2 0,01 0,00 0,3 0,01 0,10 C6 cut 1,3 0,06 0,00 1,3 0,06 0,44 C7cut 2,1 0,09 0,01 2,1 0,09 0,71 C8 1,7 0,08 0,01 1,7 0,08 0,60 C9 4,30,19 0,02 4,3 0,19 1,47 H2S COS CH3SH 16,3 0,73 610 0,061 0,2 0,009 80,001 16,1 0,72 5,49 C2H5SH 81,2 3,62 3042 0,304 0,3 0,014 12 0,001 80,93,61 27,64 C3H7SH 43,9 1,96 1645 0,165 0,9 0,040 34 0,003 43,0 1,9214,70 C4H9SH 4,7 0,21 174 0,017 0,7 0,029 25 0,003 4,0 0,18 1,36 CS2 SO2SX CO H2 O2 H2O 135 6,02 0,51 135 6,04 0,51 27 1,22 9,31 Flow Nm³/h26699 100,00 26434 100,00 293 100,00 Flow kg/h 23698 23142 293 FlowKgmole/h 1191 1179 578 Flow MMSCFD 23,917 23,679 13 Mole Wt Kg/Kg 19,8919,16 44,27 mole Temp. ° C. 50 50 57 Pressure bar 24,9 24,6 1,9 (abs)Density Kg/m³ Vap. Frac — 1,0 1 1,0 Line No.: 13 14 15 Process ResidualClaus Gas Hydrogenated Residual Claus Exhaust Gas Stream toHydrogenation Gas to Tail Gas Absorption to Postcombustion Phase gas gasgas Components Nm³/h kg Mole/h ppm V Vol % Nm³/h kg Mole/h ppm V Vol %Nm³/h kg Mole/h ppm V Vol % CO2 6026 268,84 17,61 25958 1158,10 42,8223362 1042,29 43,23 N2 17220 768,27 50,31 21420 955,65 35,34 21420955,65 39,64 CH4 40,9 1,93 0,07 41 1,83 0,08 C2H6 18,2 0,81 0,03 18 0,810,03 C3H8 3,5 0,16 0,01 4 0,16 0,01 i-C4 n-C4 i-C5 n-C5 C6 cut C7 cut C8C9 H2S 137 6,09 0,40 757,7 33,81 1,25 27,02 1,21 500 0,05 COS 60 2,670,17 3,8 0,17 0,01 3,76 0,17 70 0,01 CH3SH 0,97 0,04 0,00 0,97 0,04 0,00C2H5SH 5,15 0,23 0,01 5,15 0,23 95 0,01 C3H7SH 0,42 0,02 0,00 0,42 0,028 0,00 C4H9SH CS2 7 0,33 0,02 SO2 71 3,16 0,21 SX 14 0,61 0,04 CO 63428,30 1,85 99,72 4,45 0,16 99,72 4,45 0,18 H2 372 16,61 1,09 1156,151,58 1,91 1156,1 51,58 2,14 O2 H2O 9686 432,15 28,30 11154 497,62 18,407898 352,35 14,62 Flow Nm³/h 34227 100,00 60618 100,00 54035 100,00 Flowkg/h 42578 88170 79345 Flow Kgmole/h 1527 2704 2411 Flow MMSCFD 3154,301 48,405 Mole Wt Kg/Kg 27,88 32,60 32,91 mole Temp. ° C. 165 175 5,Pressure bar 1,3 1,2 1,1 (abs) Density Kg/m³ Vap. Frac — 1,0 1,0 1,0Line No.: 17 18 19 Process Loaded Regenerated Preloaded Stream MDEA MDEAMDEA Phase liquid liquid liquid Components kg/h kgmole/h Wt. % kg/hkgmole/h Wt. % kg/h kgmole/h Wt. % CO2 11177,6 253,98 2,62 121,1 2,80,03 5217,9 118,6 1,26 N2 11,3 0,40 0,00 CH4 342,8 21,37 0,08 C2H6 42,71,42 0,01 C3H8 36,2 0,82 0,01 i-C4 1,5 0,03 0,00 n-C4 4,9 0,08 0,00 i-C50,7 0,01 0,00 n-C5 0,7 0,01 0,00 C6 cut 0,9 0,01 0,00 C7 cut 0,1 0,000,00 C8 0,0 0,00 0,00 C9 0,3 0,00 0,00 H2S 9490,2 278,47 2,23 93,8 2,80,02 1204,8 35,4 0,29 COS 2,3 0,04 0,00 CH3SH 4,0 0,08 0,00 C2H5SH 49,00,06 0,00 C3H7SH 4,3 0,06 0,00 C4H9SH 0,2 0,00 0,00 CS2 SO2 SX CO H2 O2MDEA 121440 1019 28,51 121440 1019 29,98 121440 1019 29,3 H2O 28334015727 66,52 283360 15728 69,96 286616 15909 69,15 Flow m³/h 416,4 100,0400,2 100,0 409,6 100,0 Flow kg/h 425950 405015 414479 Flow kgmole/h17304 16753 17082 Flow MMSCFD — — — Molar M. kg/ 47,9 48,4 48,0 kgmole T° C. 32,0 8,0 9,0 P (abs.) bar 68,0 8,0 9,0 (abs) Density kg/m³ 10231012 1012 Vap. Frac. — 0,0 0,0 0,0

Corresponding to the values represented in the Table, crude gas isintroduced via line (1) into a first absorption column (21), in whichthe H₂S obtained is washed out except for a residual content of 484ppmV. For this purpose, the solvent stream (16) preloaded with H₂S andCO₂ in the tail gas absorption plant (29) is sufficient, so that washingin the absorption column (21) does not require an additional amount ofsolvent as compared to the amount required in the tail gas plant (29).The roughly desulfurized crude gas (2) still contains a large part (84%)of the CO₂ contained in the crude gas in addition to the residualcontent of H₂S, and also a large part of the mercaptan contained in thecrude gas.

From the absorption column (21), a solvent stream (17) highly loadedwith H₂S is withdrawn and supplied to a regeneration plant (22). Sincethe solvent stream is by 47% smaller than in the example described inthe unpublished prior art, the energy consumption for the regenerationlikewise is smaller by 47%.

From the regeneration plant (22) a first small gas stream (3), whichconsists of 95 vol-% hydrocarbon and 1 vol-% CO₂ with about 1 vol-%sulfur and mercaptan, is directly supplied to the Claus plant (27).

A second, larger gas stream (4), which consists of 50.5 vol-% H₂S and 46vol-% CO₂, likewise is directly supplied to the Claus plant (27).

The roughly desulfurized crude gas is withdrawn from the absorptioncolumn (21) as second gas stream (2) and supplied to a second washingstage (23) comprising absorption and regeneration. Since in this secondwashing stage (23) only a very small amount of H₂S must be washed outapart from CO₂, the required amount of solvent here is distinctlysmaller than in the numerical example in the unpublished prior art,namely smaller by 45%, so that here as well 45% less regeneration energyis required. From this second washing stage, a first gas stream (6) iswithdrawn, which consists of 77 vol-% hydrocarbon and 18.6 vol-% CO₂,and which in the Claus plant (27) is utilized as fuel gas. A second gasstream from the absorption plant (23), which contains 90.8 vol-% CO₂,1.95 vol-% H₂S and 0.1 vol-% mercaptan, is supplied to a hydrogenation(28) via line (7). As third gas stream (5), the valuable gas with thelargest part of the mercaptan is withdrawn from the second washing stage(23), cooled (24) and supplied to an adsorption (25) via line (8). Thegas stream (10) containing mercaptan is subjected to a physical washingstage (26), from which the coadsorbed valuable gas is recovered as fuelgas via line (11), and the highly concentrated mercaptan gas is suppliedto the Claus plant (27) via line (12). The mercaptan stream is recoveredin the regeneration of the Purisol solvent. The amount is small, butwith a very high mercaptan concentration of 49 vol-%. In the Claus plant(27), the mercaptan is burnt completely. The resulting SO₂ is reactedwith the H₂S from the sour gas of line (4) to obtain sulfur. The liquidsulfur obtained is withdrawn via line (16) and supplied to a furtheruse. The residual gas of the Claus plant chiefly consists of thecomponents CO₂, N₂ and H₂O and is withdrawn via line (15).

1. A process of cleaning hydrocarbonaceous gas, in which a first small gas stream (3), which substantially consists of hydrocarbon and carbon dioxide, as well as a second larger gas stream (4), which substantially consists of hydrogen sulfide, carbon dioxide and small amounts of mercaptan, is introduced into a Claus plant (27), characterized in that before the absorption and regeneration plant (23) operated at a pressure of the feed gas of 20-80 bar abs another absorption plant (21) is provided, which operates with a selective solvent at the same pressure of 20-80 bar and which roughly desulfurizes the feed gas to 100-10,000 ppmV H₂S, a solvent stream (17) loaded with hydrogen sulfide being withdrawn from this preceding absorption plant (21) and being supplied to a succeeding regeneration (22), that from the preceding absorption plant (21) a third gas stream (2), the roughly desulfurized crude gas, is supplied to the absorption and regeneration plant (23), and from this absorption and regeneration plant (23) the valuable gas (5) is withdrawn, which is supplied to a further use.
 2. The process as claimed in claim 1, characterized in that the second gas stream (4), which is supplied from the regeneration (22) to the Claus plant (27), consists of 20 to 90 vol-% hydrogen sulfide, maximally 80 vol-% carbon dioxide and small amounts of mercaptan.
 3. The process as claimed in claims 1 to 2, characterized in that the first small gas stream (3), which is supplied from the regeneration (22) to the Claus plant (27), consists of up to 95 vol-% hydrocarbon and up to 30 vol-% carbon dioxide.
 4. The process as claimed in claims 1 to 3, characterized in that from the regeneration plant (22) an unloaded stream (18) of solvent is supplied to the tail gas absorption plant (29).
 5. The process as claimed in claims 1 to 4, characterized in that from the tail gas absorption plant (29) a solvent stream (16) loaded with hydrogen sulfide and carbon dioxide is supplied to the preceding absorption plant (21).
 6. The process as claimed in claims 1 to 5, characterized in that from the absorption and regeneration plant (23) a first hydrocarbonaceous gas stream (6) is wholly or partly supplied to the hydrogenation plant (28).
 7. The process as claimed in claims 1 to 6, characterized in that from the absorption and regeneration plant (23) a second gas stream (7) containing carbon dioxide is supplied to the hydrogenation plant (28).
 8. The process as claimed in claims 1 to 7, characterized in that from the absorption and regeneration plant (23) the first hydrocarbonaceous gas stream (6) is wholly or partly introduced into the Claus plant (27).
 9. The process as claimed in claims 1 to 8, characterized in that as solvent of the preceding absorption plant (21) methyldiethanolamine (MDEA) is used. 